The Office of Fair Trading (OFT) has announced that it will investigate
whether children are being unfairly pressured to buy additional content in
'free' app and web-based games.

The decision comes after several high-profile cases where children have racked up large bills buying virtual currency, gems or fruit in games that their parents thought were free.

Martin Lewis, from Moneysavingexpert, said that "something is going wrong in the system when games such as My Little Pony, which are obviously targeted at young children, bait kids with £69 purchases of a mountain of gems."

The OFT is demanding information from the companies concerned, but parents who allow their children to play on such games will need more immediate protection. Follow the pointers below to ensure your children don't rack up bills online.

Protect your password

. Letting youngsters sit on your knee while you use your smartphone or tablet means they're likely to know your password, and that can be expensive. Make sure you change your passwords regularly.

Updating the software on an iPad or iPhone can be done on the device itself, and should offer you additional protection. To check if a newer version is available to download and install, parents should go to the 'Settings' menu, scroll down and select 'General', then choose 'Software Update.

If you choose to update when you are not connected to your computer, you will need to use Wi-Fi instead of 3G, as the file size will be too big.

Alternatively, if you connect your device to your computer, a pop-up window will say if your software is out of date and you will be prompted to install the latest version.

Use parental controls

Ask your mobile provider about financial and parental controls that may be available for your device.

Disable the purchase function

To disable the in-app purchases function on your Apple device, go to "Settings", select "General", tap "Restrictions" and select "Enable Restrictions". Here you must create a unique four-digit passcode, then scroll down to "Allowed Content" and turn off "In-app Purchases".

Bear in mind that unless you adjust the time necessary before a password is required to purchase content, it will automatically allocate a 15-minute time limit. This will mean that if it has been less than a quarter of an hour since you downloaded the app or made an in-app purchase, your children will not be required to type in your password again, potentially racking up a huge bill without inputting any additional details.

Use Airplane Mode

Even if you aren't flying, this will block all downloads and in-app purchases. To do this on an iPhone or iPad, go to "General", select "Settings" and then turn "Airplane Mode" to the on setting.

Use a Gift Card

For the parents of teenagers who wish to make purchases on their own device, but who do not have their own bank account, using an iTunes gift card instead of your credit card will help avoid unwanted costs. If you always use vouchers for your iTunes account, instead of linking a credit or debit card to it, it will never charge you more than is on the vouchers, no matter how many 'Smurfberries' your child attempts to buy.

Get Google savvy

It is not only Apple products that can leave parents facing potentially hefty bills. With Google's Android, in-app purchasing is also problem, but, as with the iPhone and iPad, there is protection available.

To ensure your Android is safe, always activate the "Screen lock" function, which will force users to enter a pattern, pin or a password on the device each time an item is to be bought. To set this up simply go to "Settings" then "Security" and then you can choose and set it.

Similarly, removing bank details from "Google Checkout" can stop this function from being exploited. To remove your information, go to the "Google Checkout" site and log into your account.

On the left of the screen will be a link called "Edit payment methods". Follow that and you will get a list of your accounts. Remove your financial details with the delete button. The Android Market will pull your payment information directly from Google Checkout so no apps can be purchased by yourself or your children. For future purchases, simply re-enter the details on your account.

Ask for help

If you do get stung, contact your mobile provider and ask them (politely!) to cut the bill as a gesture of goodwill.